The present invention concerns a method of securing a sealing layer to a support, particularly a sheet of synthetic resin to the outer surface of a roof.
To cover roofs that extend horizontally or at a comparatively small angle of inclination it is nowadays common practice to use a sealing layer consisting of a sheet of polyvinyl chloride. A sheet of this kind is in itself a good protection against penetration of water into the framework of the roof. The sealing layer, which usually is laid on top of a heat-insulating layer, naturally must be anchored so as not to be blown off or slide away from the roof. For this purpose, the sealing layer is secured with the aid of plates or mouldings of sheet metal or plastics through which are passed fastening means, such as screws or nails which are screwed (nailed) to the support.
The sealing layer may in principle be secured to the support in two different ways. Either each plate is initially secured to the support by means of a screw or nail, whereafter the sealing layer is arranged on top of the plates and secured thereto by an adhesive. Alternatively, the sealing layer may first be deposited on top of the roof, whereafter the plates are placed on top of the sealing layer, and a screw or nail is then passed through each plate, the sealing layer, and any other roof-covering layers, and fastened to the support.
The first-mentioned method, i.e. positioning of the sealing layer on top of the plates, offers the advantage of providing a roof that with considerable certainty is completely watertight. However, it is a complicated task to secure the sealing layer of the plates as their exact locations underneath the synthetic resin film are difficult to keep account of. Furthermore, the sucking force generated by the wind and to which the external face of the sealing layer is exposed may gradually cause ripping off of the sealing layer from the plates as a result of the so called peeling effect.
To guarantee that the sealing layer is secured to the underlying layers, the second one of the above-mentioned methods has often been chosen, i.e. positioning of the plates on top of the sealing layer. However, another problem arises in this case, as it becomes difficult to obtain a completely watertight joint in the area around each plate and its associated screw or nail. In order to make the joint tight, one has therefore been forced to place on top of each plate a piece of a synthetic resin film or a strip on top of a row of plates and secure the film by an adhesive to the sealing layer. However, it means a considerable complication to have to produce such film pieces and also more equipment and material must be brought onto the roof. Also, the inherent springiness of a roof of the kind described causes it to bend when walked on, and as a consequence thereof, the plates may be depressed to such a degree that the screws or nails passing through the plates will be displaced upwards, somewhat above the plates and possibly also penetrate through the synthetic resin pieces covering the plates. If this happens, water may easily seep in through the openings thus formed and trickle along the screws or nails into the substructure and cause considerable damage thereto.